AOU filming in South Korea from March 20 through April 12.
22 days of location shooting suggests to me that Korea is going to be VERY important to the plot of this movie.

I don't think this is going to be a case of throwaway scenes and characters, like the overhyped IM3 location shoots in Beijing.

Yeah they're filming in SK but it doesn't mean she's gonna be in it for the majority of the schedule. Here's a K-entertainment site that discusses the news.

"In addition, Walt Disney said, "Soo Hyun has been ultimately cast as a supporting actress among the minor characters of 'Avengers 2.'" She will be taking part in the filming in Korea planned for April."